The present invention relates to integrated circuits and fabrication techniques for forming field oxide (FOX) regions on the integrated circuit substrate. More particularly, the present invention relates to fabrication techniques for forming shallow trench isolation (STI) regions on the integrated circuit substrate.
The processes for fabricating semiconductor devices includes process steps for providing isolation regions that contain dielectric materials that provide the necessary protection for assuring proper function of the formed electronic integrated circuit design. The process includes LOCOS which is localized oxidation of silicon. This process typically begins by depositing a silicon nitride layer over a silicon dioxide layer (barrier oxide) to a thickness in the range of 0.05 xcexcm. to 0.10 xcexcm. The silicon nitride is typically deposited using low-pressure chemical vapor deposition (LPCVD) techniques. A photoresist mask layer, comprising any appropriate commercially available photoresist material known in the industry, is then deposited over the silicon nitride layer The photoresist mask layer is then patterned for forming isolation trenches. Upon etching, the isolation trench regions are formed adjacent silicon oxide layer and the silicon nitride layer and a portion of the photoresist layer. Typically, in order to form the trench regions, the upper surface of the substrate is etched a small amount, approximately 0.25 xcexcm. An oxide layer is formed in the isolation regions by depositing a thick pad of silicon dioxide using tetraethylorthosilicate (TEOS) as the source for deposition of silicon dioxide. The thickness of the oxide pad, also referred to as a field oxide (FOX) pad, is in the range of 1.2 xcexcm to 1.5 xcexcm. The process further includes polishing of the formed isolation pads to a surface level and thickness substantially even with the silicon nitride level. Subsequent to formation of the oxide pads the silicon nitride and silicon dioxide layer regions are removed by wet etching to expose the active region which will be used to form the various integrated circuit components. The wet etching is typically done using hot phosphoric acid to first etch the silicon nitride layer, then by dipping the substrate in a hydrofluoric acid (HF) dip to etch the silicon dioxide layer.
As seen from the foregoing, formation of the trench region, in accordance with prior art techniques, erodes the adjacent barrier oxide and silicon nitride layers protecting the active regions. Thus, a need is seen to exist for a method of forming the isolation trenches without eroding the adjacent silicon nitride pads and barrier oxide that overlay the active regions of the semiconductor structure.
Accordingly, a primary object of the present invention is to provide a method for forming isolation trenches such that the adjacent structure protecting the active semiconductor substrate is not eroded during etching processes used to form the trench regions.
Accordingly, the foregoing object is accomplished by providing a semiconductor substrate member fabricated having a thin barrier oxide layer on which are fabricated a plurality of spaced apart silicon nitride pads. The regions between the spaced apart nitride pads delineate U-shaped regions for forming shallow isolation trenches and are layered with silicon oxide and polysilicon. The U-shaped regions provide a buffer region of oxide and polysilicon material adjacent opposing silicon nitride pads that prevent erosion of the nitride during etch formation of the isolation trench. The polysilicon is further etched to form a wider, second U-shaped region having sloped sidewalls that provide opposing spacerforming buffer material that facilitates forming a V-shaped isolation trench region into the semiconductor substrate member a predetermined depth without eroding the silicon nitride pads. The V-shaped trench is subsequently filled with silicon dioxide that is grown by a hot thermal oxide process. The upper portion of the V-shaped isolation trench may be further filled with deposited silicon dioxide followed by a chemical mechanical polishing process.
Other features of the present invention are disclosed or apparent in the section entitled: xe2x80x9cDETAILED DESCRIPTION OF THE INVENTIONxe2x80x9d.